(a) Field of the Invention
The present invention relates to a shift control method and apparatus of an automatic transmission that control a shift from one speed, achieved by engagement of first and second frictional elements, to another speed, achieved by engagement of third and fourth frictional elements.
(b) Description of the Related Art
Generally, one frictional element is released and another frictional element is engaged during a clutch-to-clutch shift control. However, during some specific skip-shifting processes, two frictional elements may be released and two other frictional elements may be engaged.
Particularly, in the case of a kick-down 8 to 2 skip shift where six speed steps are shifted, generally two frictional elements must be released and two other frictional elements must be engaged. Controlling this shift is difficult.
Therefore, two successive shifting processes are sometimes used. For example, a 7 to 2 shift is performed after an 8 to 7 shift is completed so as to perform an 8 to 2 shift. However, this takes additional time, and deteriorates shift feel.
Another proposed solution is to overlap the two shifting processes However, torque of the middle speed may be generated and a double shift feel may be felt.
In addition, since the shift is controlled according only to rotation speed of a turbine, the shift may not be precisely controlled.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.